1. Field of the Disclosed and Claimed Inventive Concepts
The presently disclosed and/or claimed inventive process(es), procedure(s), method(s), product(s), result(s), and/or concept(s) (collectively hereinafter referred to as the “presently disclosed and/or claimed inventive concept(s)”) relates generally to methods for the preparation of alkyl hydroxyalkyl cellulose ethers. More particularly, but not by way of limitation, the presently disclosed and/or claimed inventive concept(s) further relate to the use of such alkyl hydroxyalkyl cellulose ethers in the preparation and use of mortars and other cement-based systems. The presently disclosed and/or claimed inventive concept(s) also relates generally to a hydraulic and/or dry cement mortar composition with a prolonged open time, more particularly, the composition comprises at least one retarder, and/or at least one accelerator, and such alkyl hydroxyalkyl cellulose ethers. The presently disclosed and/or claimed inventive concept(s) also relates generally to dry mortars containing encapsulated calcium chloride, and such alkyl hydroxyalkyl cellulose ethers, and their use in preparing mortar materials for use in construction, and more particularly, their preparation and use in cold weather environments.
2. Background and Applicable Aspects of the Presently Disclosed and Claimed Inventive Concept(s)
Cellulosic ethers (CEs) are a class of water-soluble organic polymers utilized in a variety of technology applications such as building and construction, pharmaceuticals, energy, electronics, the food and beverage industry, surface coatings and paint. CEs provide a variety of desired physical and rheological characteristics. One such example is the ability of CEs to increase the viscosity of aqueous media. Alkyl, hydroxyalkyl, or alkylhydroxyalkyl CEs have been extensively utilized in cement-based applications such as cementitious tile adhesives, tile grouts, etc. The wide-spread usage of alkylhydroxyalkyl CEs in the building and construction industry is in large part due to the unique rheological properties attained with these organic polymers. They improve physical properties such as viscosity, workability, adhesion to substrate, open time, consistency, water-retention, stickiness, and sag resistance.
Processes for preparing CEs are well-known in the art. Alkyl hydroxyalkyl CEs are commonly prepared by reacting an alkylene oxide and an alkyl halogenide at the same time during the etherification stage of the process.
In the synthesis of alkylhydroxyalkyl CEs, the cellulosic anhydroglucose hydroxyls are subjected to alkaline conditions and reacted with etherification agents. The properties and characteristics of the final polymer formed will be determined by the choice of etherification agent(s) as well as the process conditions utilized. When an alkylene oxide/oxirane is reacted with a cellulosic hydroxyl under alkaline conditions, a reactive intermediate is formed. This intermediate can further react with any etherification agents present in the reaction medium. If reaction occurs further with an alkylene oxide/oxirane, oligoether chains can result. If alkyl halogenides or other etherification agents that do not generate a reactive functional group are reacted the resultant ether cannot react further. This is commonly referred to as capping.
It has been found that % unsubstituted anhydroglucose units, enzyme unsubstituted weight %, and blockiness index can be controlled to a great extent by using a modified process for alkylhydroxyalkyl CE synthesis, as described herein. The hydroxyalkyl CEs obtained demonstrate much faster setting times in cement-based systems in comparison to conventional/hitherto existing/standard CEs/not using the alkyl hydroxyalkyl cellulose ether prepared as described above and result in improved strength values. These CE compositions can be used in cement-based applications to provide rheological advantages such as easy workability and improvements in viscosity, workability, open time, consistency, water-retention, stickiness, and sag resistance while at the same time providing desired setting time and strength profiles.
In addition, for mortar applications, evaporation and absorption of water through porous substrates on which the mortar is applied lead to a depletion of water in the wet mortar over time, which can result in very short open time, correction time, and even issues with adhesion to the substrate. Open time of a mortar is the time in which a tile can still be placed in the applied mortar and sufficient wetting of the tile with mortar is assured. The end of the open time is indicated by having insufficient wetting of mortar on the backside of the tile. Open time is affected by the amount of drying, chemical and physical reactions related to the setting of the cement, and effects of other additives like cellulose ethers and redispersible polymer powders. Additionally, a lack of sufficient water for the proper hydration of cement results in insufficient and incomplete strength development of the mortar.
Cellulose ethers are often added to the mortar to provide water retention, thus reducing water loss due to evaporation and absorption of the substrate and providing constant workability, acceptable correction and open time and proper strength development.
A method of extending open time by adding organic and/or inorganic cement hydration retarders to a cement mortar has widely been used. Through the addition of retarders, the hydration reactions are decelerated or delayed. Consequently the setting and hardening of the mortar is shifted and open time is prolonged. Setting time is defined in ASTM C266-65. Basically setting time is the time a mortar takes to set or harden at a given thickness. For construction using a cement-based hydraulic composition such as mortar or concrete, the control of setting time is desired with a view to ensuring workability, shortening the construction time and simplifying a curing facility. Such decelerated cement hydration, and delayed setting time, due to the presence of a retarder, leads to a higher risk of water loss resulting in insufficient strength development.
Thus, there is a need to have a mortar having a long open time without unduly delaying the setting time. Surprisingly, it has been found that the positive gain in open time by usage of a retarder is not reversed if an accelerator is added to compensate for the cement setting time retardation resulting from the retarder. It has even been found that a retarder-accelerator combination can generate a synergistic effect, meaning that the combination can even have a longer open time compared with a retarder alone.
Further, calcium chloride is generally known as an effective accelerator for cementitious systems. Calcium chloride compounds such as anhydrous CaCl2, CaCl2.H2O, CaCl2.2H2O, and CaCl2.4H2O are exothermic when hydrated, making them especially suitable for cold weather applications. However, such calcium chloride compounds are each hygroscopic and deliquescent (with anhydrous CaCl2 being very hygroscopic and deliquescent) and can each form an aqueous solution when exposed to humid air, making it difficult to handle. Thus, such calcium chloride compounds, when stored in humid air, each soon become a hydrated solution which is unsuitable for use in a dry mortar application. For this reason, calcium formate, which is not as hygroscopic, is typically used in dry mortar applications instead of calcium chloride. However, calcium formate is an inferior accelerator as compared to calcium chloride. For example, at least about 0.3 wt % of calcium formate typically has to be present in a mortar before any acceleration begins, whereas as little as 0.05 wt % of calcium chloride in a mortar starts the acceleration. Also, regarding acceleration, around 0.3 wt % of calcium chloride is equivalent to about 0.7 wt % of calcium formate, with each amount typically providing adequate acceleration.
Further, preparation of mortar at low temperatures (below about 15° C.) can be very challenging due to extremely slow cement hydration rates at low temperatures. In such low temperature environments, it often becomes necessary to add heat to the system through: heating the water added to the dry mortar or using heat lamps or heaters to heat the environment or protect the curing mortar with blankets or the like. It is common to use accelerators to ensure a fast hydration of the mortar. So, anhydrous calcium chloride is not only an efficient accelerator but also provides heat to the system when dissolved in water. However, the use of calcium chloride is difficult, as discussed above due to its hygroscopic nature. The water uptake of such calcium chloride compounds present in a dry mortar mix will cause lump formation and caking of the mix, resulting in deteriorated powder properties. The water uptake will also result in decreased active calcium chloride content, undesirable pre-hydration of the cement, and will make the dry mix more difficult to handle. It has been found that at least partially encapsulating such calcium chloride compounds can overcome these deficiencies upon introduction into a dry mortar composition, wherein hydration of the calcium chloride is prevented or minimized up to the time a wet mortar is prepared.